p.10
Reaction of Applied Phosphorus in Soils
What happens to H2PO4- under acidic soil conditions with Al(OH)3?
It reacts to form variscite and releases H2O.
p.14
Factors Affecting Phosphorus Availability
What is another method to maintain phosphorus availability?
Regulation of the fixation in both added and native phosphorus.
p.9
Application Methods for Phosphorus Fertilizers
What is the primary objective of any fertilizer placement method?
To ensure positional availability for many plant roots throughout the growing season.
How does phosphorus enter the soil?
Through weathering of rocks, decomposition of organic matter, and application of fertilizers.
p.12
pH and Phosphate Ion Availability
What determines the availability of phosphorus to plants?
The ionic form of the element.
p.8
Reaction of Applied Phosphorus in Soils
What happens to phosphorus at certain pH levels?
It can form fixed forms such as Al-P, Fe-P, and Ca-P.
p.11
Reaction of Applied Phosphorus in Soils
What is the significance of hydroxyapatite in soils?
It is a stable form of phosphorus that can be utilized by plants.
p.5
Sources of Phosphorus Loss
What is fixation in the context of phosphorus loss?
Fixation refers to the process where phosphorus becomes unavailable due to binding with soil particles.
Why is phosphorus important in ecosystems?
It is a vital nutrient for plant growth and is essential for the formation of DNA, RNA, and ATP.
What are some human impacts on the phosphorus cycle?
Overuse of fertilizers can lead to runoff, causing water pollution and algal blooms.
p.13
pH and Phosphate Ion Availability
What happens at pH 6.5 concerning phosphorus availability?
Formation of insoluble calcium salts renders phosphorus unavailable.
p.7
Factors Affecting Phosphorus Availability
How does water solubility of phosphate minerals depend on soil conditions?
It is very dependent upon soil pH.
p.14
Phosphorus Fertilizer Materials
What happens to nutrient levels in the soil with continued application of phosphate fertilizer?
Nutrient levels in the soil increase.
p.13
pH and Phosphate Ion Availability
What occurs at higher pH values regarding phosphorus?
Some phosphorus is released and the fixing capacity is reduced.
What happens to phosphorus when organisms die?
Phosphorus is returned to the soil through decomposition, making it available for new plant growth.
p.8
Soil Chemical Properties
What elements influence phosphorus availability in soil?
Aluminum (Al), Iron (Fe), and Calcium (Ca).
p.11
Reaction of Applied Phosphorus in Soils
What role does CaCO3 play in the reaction with H2PO4-?
It reacts with H2PO4- and OH- to form hydroxyapatite.
p.7
Factors Affecting Phosphorus Availability
What effect does applying phosphorus with ammonium sulfate have?
It increases phosphorus uptake due to high nitrogen concentrations.
p.8
Soil Physical and Chemical Properties
How does soil texture influence phosphorus fertilizers?
It affects soil diffusion rate, rate of chemical reaction, and the reaction products formed.
p.14
Phosphorus Fertilizer Materials
What is one method to maintain sufficient available phosphorus in the soil?
Addition of phosphorus containing fertilizer.
p.3
Forms of Phosphorus in Soils
Can organic phosphorus forms be taken up by plants?
Yes, but this is a less common condition.
p.5
Sources of Phosphorus Loss
How does erosion contribute to phosphorus loss in soils?
Erosion can wash away topsoil, which contains phosphorus.
What role do plants play in the phosphorus cycle?
Plants absorb phosphorus from the soil, which is then transferred through the food chain.
p.11
Reaction of Applied Phosphorus in Soils
What is the reaction that occurs under alkaline soil conditions involving H2PO4-?
H2PO4- + CaCO3 + OH- → Ca10(PO4)6(OH)2 + H2O (hydroxyapatite).
p.12
pH and Phosphate Ion Availability
How is the ionic form of phosphorus determined?
By the pH of the solution in which the ion is found.
p.5
Sources of Phosphorus Loss
What are some sources of phosphorus loss in soils?
Decomposition of crop residues, manure, P fertilizer application, weathering of P-bearing minerals.
p.3
Forms of Phosphorus in Soils
What are the primary forms of phosphorus available for plant uptake?
The orthophosphates, H2PO4- and HPO4^2-.
p.11
Reaction of Applied Phosphorus in Soils
What is the product formed from the reaction of H2PO4- under alkaline conditions?
Hydroxyapatite (Ca10(PO4)6(OH)2).
p.12
pH and Phosphate Ion Availability
What happens to the ionic forms of phosphorus as pH increases?
HPO4^2- is present first, then PO4^3- dominates.
p.5
Sources of Phosphorus Loss
How does crop removal contribute to phosphorus loss?
Phosphorus is taken up by crops and removed from the soil when harvested.
p.7
Factors Affecting Phosphorus Availability
How does particle size affect phosphorus fertilizer effectiveness?
It is closely related to water solubility.
p.7
Factors Affecting Phosphorus Availability
What is the effect of applying phosphorus with lime?
It reduces phosphorus effectiveness.
p.10
Reaction of Applied Phosphorus in Soils
What is the role of H+ in the reactions involving H2PO4-?
It participates in the formation of variscite and strengite.
p.12
pH and Phosphate Ion Availability
What is the relationship between pH and phosphate ions?
As pH increases, the forms of phosphate ions change from H2PO4- to HPO4^2- and then to PO4^3-.
What is the Phosphorus cycle?
The process through which phosphorus moves through the environment, including soil, water, and living organisms.
p.13
pH and Phosphate Ion Availability
What happens to phosphorus at pH 6.5?
Much of the phosphorus is still chemically combined with iron and aluminum.
p.5
Factors Affecting Phosphorus Availability
What role does soil organic matter (OM) play in phosphorus availability?
Soil OM can influence the availability of phosphorus in soils.
